This invention relates to a valve block assembly of the kind having multiple inlets and a single outlet. Such assemblies find particular application in protein sequencers.
Wittman-Liebold, U.S. Pat. No. 4,008,736 describes a valve arrangement in which a common conduit is formed in the valve block. All delivery valve sites lie on the same surface and are connected by zig-zagging portions of the conduit. While this type of common conduit may be cleaned by flushing, it cannot be cleaned easily with a wire. It is also difficult to machine.
Graffunder, U.S. Pat. No. 4,168,724 replaced the slider valves of the U.S. Pat. No. 4,008,736 with diaphragm valves. These valves are closed by fluid pressure in an actuator chamber adjacent to the diaphragm, and opened by evacuating the chamber. The zigzag sections of the common conduit intersect at the surface of the valve block. All delivery valve sites lie on the same surface.
This apparatus has several disadvantages. First, it is necessary to provide vacuum and high pressure sources. Second, the diaphragm has a tendency to cold flow into the common conduit at the point of intersection, requiring that it be moved a greater distance in order to open the valve. This in turn places greater demands on the evacuation system, and increases the wear and tear on the diaphragm.
Hunkapiller, U.S. Pat. No. 4,558,845 replaces the zigzag sections of Wittman-Liebold with straight sections which are easier to clean and to machine. However, each valve site is placed on a separate block, and the common conduit is alternately a channel in a block and tubing exposed to the atmosphere.
Hunkapiller also replaced Wittmann's actuation mechanism with a plunger that is spring-biased to a closed position. A solenoid device is used to draw the plunger to an open position. Since Hunkapiller retains the narrow access port of the previously described apparatus, his valve is likewise subject to the problem of membrane "cold flow".